Complete amazing feats to unlock Noble Team helmets for your Avatar.
Carter's Helmet - Clear a Campaign mission on Legendary without dying
Unlocking Carter's Helmet may seem a difficult task at first, but there's a bit of an exploit you can use to easily unlock it. This trick works at the time of this writing, but may be addressed in a future patch.
Select any mission on Legendary (if you're looking for an easy one, go with Winter Contingency) and fight your way to the end, dying as many times as this takes. Then, when you reach the final checkpoint, pause the game and select the Save and Quit option. With that, reload your save and complete the mission from the final checkpoint without dying. The game will consider this completing the mission on Legendary without dying and you'll unlock this award.
Jun's Helmet - Kill 100 enemies in a row without dying in either Campaign or Firefight
For an easy time with this one, download the custom Firefight variant here:
To download, ensure you're logged in with your main Gamertag and then click the Download link in the bottom-left corner of the description panel to add the file to your Halo: Reach active transfer list. The next time you start up the game, the file will automatically download and then be available for selection.
To play the variant, select 'Firefight' on the main menu, then enter Gametype and select 'SuperCheats.com' from the list. Play on Courtyard and Jetpack around with a Rocket Launcher to rack up an impressive kill count with minimal effort.
Emile's Helmet - Earn a Bulltrue medal in either multiplayer or Firefight Matchmaking
To earn a Bulltrue medal, you must kill an enemy who is equipped with an Energy Sword and in the act of a lunge. Play enough and you'll unlock this one eventually. A good playlist to use is the Living Dead playlist for the Infection game type, as you're sure to be pitted against the Energy Sword-wielding Infected at some point.
Jorge's Helmet - Earn a Killtacular in multiplayer Matchmaking
To earn a Killtacular medal, you must kill five enemies in a short period of time. Unlocking this item requires luck above all else. Good playlists to use are Team SWAT and Multi-Team.
Kat's Helmet - Avenge a teammate's death in multiplayer Matchmaking
Unlocking this item requires earning an Avenger medal. To earn this medal, you must kill an enemy shortly after that enemy kills one of your teammates. Keep playing multiplayer and you're sure to unlock this one at some point.